DESCRIPTION: This proposal aims at using x-ray crystallography to determine the structures of DNA complexes of two proteins, Pit-1 and Extradenticle (Exd). Pit-1 is involved in development of the pituitary gland in mammals and Exd in the specification of body parts in Drosophila. Both proteins contain homeodomains and the focus of the proposal is to understand how the specificity of homeodomain proteins is augmented by the buildup of multiple modular interactions. Pit-1 is composed of a Pou domain that contains two DNA-binding components: a Pou-specific domain and a homeodomain. Exd is a homeodomain protein that can modulate the specificity of some other homeotic proteins. A number of different structural projects are identified in this proposal. These include the study of Pit-1 bound to different natural DNA targets, upon which it may adopt different conformations. Structural analysis of Exd will include study of the Exd homeodomain bound to DNA, as well as of a fragment containing the entire homology region between Exd and the human oncoprotein Pbx1.